Radio monitoring system



Sept. 28, 1948. A. PREISMAN 2,450,018

' RADIO MONITORING SYSTEM Filed May '7, 1943 2 sheets-sheet 1 6 Maro/P 7 l 8 afer/waan@ WAVE af/vf/mrm IN VEN TOR.

fu 51E/P7" PRE/sMA/v ATToRm Sept. 28, 1948. A. PRElsMAN RADIO MONITORING SYSTEM 2 sheets-sheet 2 Filed May 7, 1945 v z 11 1,l 111| 11l I 111111 11| 111 11 11p I 111 111 1 1 1 1 l 1 1 1 1 1 l 1 1 1 11 111111P11111111 l. |11 H .|||111 1 l 1 1 1 1 IIL 1 1 1 1 1 1P 1 1 1 1 1 1| u L @1411- 1: 11 :m |11|| 1111 11 11R 2 11111111 11 11111110 7M 3 ||l1 ||||l 1111 x11Dl 7a u nW/\.| llilymllll 1T|11||| |111 l l l IIJ 1 1 I 1 ||1w i l I 1|.|1| N 1 1111 1111 1 1 1 1 1 1 I1 111111 1 1111111; du M T M. l. 4 cw Vf C 0 fwn] Ew I/ C G @ff N PK 0 R M23 N# m mi @E @ME w l W C U T TWG/C LTG 5/ 6 N ONN www u@ um Hmm mmm @am @mi L Mmmm wc w w M0 MD m6 #MM50 IN VEN TOR. HL BEI? T P/sE/SMN A 7' TURN Patented Slept-28, 1948 ,isolnsA RADIO MoNIToaING SYSTEM Albert Preisman, Flushing, N. Y., assgnor tok Federal Telephone and Radio Corporation, Newark, N. J., a corporation of Delaware Application May 7, 1943,` seriaiNo. 485,970

c claims. (ci. o-a0) The present invention relates to radio monitoring systems and more particularly to radio systems for intercepting radioA transmissiony from particular stations.

, Numerous systems have been proposed wherein a receiving station is tuned over a band of frequencies in order to locate a particular transmission station as to frequency of broadcast or transmission. In some of these proposed systems aA receiver is provided which is continuously tuned over particular frequency bands so that communications may be detected even though the frequency of transmission is periodically changed.

It is an object oi the present invention to provide a radio receiver in which the tuning is continuously varied except for regular periods of fixed tuning.

It is a further object of the invention to provide a scanning condenser which will provide intervals of xed tuning alternately with periods of variable tuning.

It is a still further object of the invention to provide a circuit for controllingY the scanning "of an oscilloscope indicatorv simultaneously with the variation in tuning of a scanning receiver.

According to a feature of my invention, a system is provided wherein a condenser is charged and discharged at particular intervals through the medium of a mechanical switching arrangement to produce a desired wave pattern for controlling the scanning of a cathode-ray oscilloscope. At the same time this mechanical control of the cathode-ray scanning circuit may be operated in timed relationship with the adjustment of mechanically variable tuning elements in a receiver so that the scanning of the beam of the oscilloscope will coincide with the changes in tuning of the receiver. Since the invention proposes the use of a receiver having intervals of fixed tuning as well as intervals of variable tuning, the mechanicalcontrol of the cathode-ray scanning circuit is arranged so as to show this fixed tuning interval as a'separate trace on the screen of the oscilloscope, and of suicient enlargement so that the single frequency received during this interval may be readily inspected. Furthermore, the invention provides means for separating this single frequency trace from the frequency band shown by the intervals of variable tuning, and for removingthis single frequency trace to a separate portion of the screen. Other means are provided for selecting from the entire wave band pictured the single frequency to be traced, and also for blanking the beam of the tube during the scanning return'periods. Thus any frequency seen on the screen inthe usual manner may be separated from the other frequencies, transferred to a separate portion of the screen, and then swept across the screen to permit close inspection of its characteristics.

A further object of the invention is the provision of a control circuit for producing the particular wave `pattern required for scanning the cathode-ray oscilloscope when applicants novel type of scanning condenser is employed.

A better understanding of the invention and the objects and features thereof may be had from the particular description made with reference to the accompanying drawings, in which:

Fig. 1 is a schematic circuit diagram illustrating a radio system incorporating the features of my invention;

Fig. 2 is a set of curves used to explain the operation of the system illustrated in Fig. 1;

Fig. 3 is a view of the scanning condenser used in the circuit of Fig. 1;

Figs. 4 and 5 are views of a cathode-ray oscilloscope screen illustrating types of indications which may be shown thereon.

In Fig. 1 is shown a receiver 6 having two tuning condensers C1 and Cz connected in parallel. The receiving circuit incorporating these condensers may be of any suitable type. C2 is a manually controlled condenser used to pre-select a desired wave band. C1 is a motor driven scanning condenser of a type hereinafter to be described, and is used periodically to tune the receiver over the wave band selected by C2.

`A motor I is provided to drive the scanning condenser Ci. synchronously controlled by the same motor 'I is a rectangular wave generator 8, which feeds pulses to three Wave spacers and Shapers 9, I0 and II. The outputs of wave spacers and Shapers 9 and I0 are fed to the grids of triodes V2 and V1 respectively. The output oflwave spacer and Shaper I I is amplified 4at I2 and then applied to the grid of a cathode-ray oscilloscope I4.

A rotating switch S1 is controlled synchronously with the condenser C1 and wave generator 8 by the motor 1 as indicated in Fig. 1. A condenser C3 in parallel with Si is alternately charged and discharged by rotation of Si and the output applied to the horizontal deflection plates of the oscilloscope I4.

The condenser Ci of Fig. l is designed as shown in Fig. 3. The rotor I5 has a portion cut-out as at ABC.. As the rotor rotates, the capacity increases luntil cut-out ABC enters the stator I6.

Over arc AC very little, if any, change in capacity should occur. If desired, an additional segment DE may be employed as shown, so that the capacity can be made to remain perfectly constant (or even decrease, depending on the design of the segment) over arc AC, since DE can be made to compensate for the fringing effect of sides AB and BC. The variation in tuning with time is shown in Fig. 2 (D). While the cut-out ABC is entering the stator I6 the frequency responsiveness of the receiver' is constant, MN of Fig. 2 (D). Further rotation increases the frequency to which the receiver is receptive from N to P, at which time the rotor I5 except for the segment DE is entirely within the stator I6. vAs'therotor leaves the stator the curve reverses, PQRZ, with another constant period QR. It willlthusbeseen that this frequency responsivenessof the-receiver 6 is constant during the periods MN and QR as the cut-out ABC is entering and leaving thestator IS, and the receiver 6 is momentarily a iix-tuned receiver.

This variation of tuning with time as shown in Fig.'2 (D) produces an output LAfrom the receiver (for signals Ydistributed through the spectrum). This output is applied te the verticaldeflection plates ofthe oscilloscope 1:4, causing'the'picture of Fig. 4 to appear, assuming a sweep frequency of conventional Asawetooth pattern :synchronized with the scanning condenser'inthe Vusualrnanner. The normal resonance curves will appear in the sweep FG Vexcept'at tIlI[,"where a'smallse'ction of the'time-wave shape corresponding to the signal Yof the Vfrequency to 'whichthe receiver' is `momentarily tuned, `will appear. By Acareful adjustment of Ithe tuning condenser'Cz in vparallel with 'the Yscanningv 'condenser C1, precise tuning of the cut-cut portionI-II willbe obtained.

The above description has assumedthe usual saw-tooth wave pattern applied ,to thehorizontal plates of the oscilloscope I'll. "If,.however,'the horizontal sweep voltage 'Ehof `Fig. ".2 '(A') iisemployed in conjunction with a'vertical deflection voltage, Fig. 2 (B) mixed with the.received signals, which have been scanned 'by the 'condenser C1 of Fig. 1 to produce fthe'tuning variation .of Fig. 2 (D), then the'picture appearing on the oscilloscope screen will be'as .in'Fig.'5, for'reasons' which will now lbe explained.

vIt willbe noted that curve portionLP ofFigJZ (D) .issimilar in form to curve .portion'LIP of Fig. 2 '(A) and that they occur during-the.-same time interval. During sweep'FJ (Fig. 15') produced -on the oscilloscope screenby .the increase in sweep voltage UM', the requencies "LM A(received during this time interval) Vproduce ,the usual picture as shown. Now, howevenduring period MN'no sweep occurs, and in additionduring this period a single frequency isbeing received due to tread MN in .Fig."2 (D). lSince no horizontal deiiecticn occurs during this period, portion HI (formed as a result ,of the continuous sweep in Fig. 4) will close vup .into .line JK of Fig. 5, and will bebrig'hter'than'the normal .resonance curves. 'Voltageincrease'NP now-completes the sweep of the beam across JG, and pictures the curve'portionlNIJ of Fig. 2(D). 'Thus a pause is produced in sweepFG atpoiritfJin Fig. 5, corresponding in duration to thetime interval MN.

As the condenser unmeshes, portion PQ of Fig. 2 (D) is not shown on the oscilloscope screen because there is no sweep voltage applied during this time interval, as shown in waveportionP'fQ of Fig. v2 (A), Whenpoint Q is` reached, or'Q' in Fig. 2 `(mythe-steady frequency QRis being traced Von '.the Ascreen V"by the increase in sweep voltage Q'R', flat portion of dotted line PZ equals QR of Fig. 2 (D), the latter reaching the same maximum as sweep LP and thus giving as long a sweep in a much shorter interval. How this wave, Fig. 2 (A), is produced will hereinafter be explained. Portion RZ is not shown on the screen because during this time the sweep voltageis a minimum, as can againbe seen from Wave portion R'Z of Fig.'2 (A). In other words, of the portion PZ of Fig. 2 (D), only the horizontal portion QR is shown on the oscilloscope screen, and furthermore this portion is swept across the lscreen to give a full-size picture of the steadiy frequency to which the receiver 6 is momentarily tuned,

C'oming'now to wave (B) of Fig. 2, it was hereinbefore stated that this wave was a vertical deiiection :voltage mixed with the received and scanned signals. During time YU this voltage is steadily positive and the sweep FG is across the upper portion of the screen. However, from `U to Sthe'application of Va 'constant negative roltage -causes sweep FG' (thelpictureinFlgf .of steady frequency QR) to operate .on 'the 'lower portion of the screen. Thus the complete picture of Fig. 5 is obtained, and propercadjustment of .the 'tuning 4condenser Cz in parallel .with .the scanning condenser C1 will spread. any .desired frequency of the received .band across-thelower portion of the'screen.

Wave'(C) .of Fig."2's applieiito thefgridoflthe oscilloscope i4 in the `conventional manner 'to blank the beam except when wanted. Theperiods of blanking .can be easily seenlby comparison lof the corresponding time intervals, "Thus the beam is'eifective during sweep periods LMNP' ,and Q'R', and blanked during the remaining time This eliminates the .return trace an'dlimproves thesharpness of thepicture obtained.

.The output of the receiver .6 resultingfrom operation of the condenser C1, is .superimposed on vertical deflection vvoltage (B), the ywave controlling the position of thepicture 4on the screen. Horizontal deflection wave (A), the .sweep .voltage, isapplied to the'horizonta'l deflection plates. Blanking wave (C) is applied to the controlgri'd ofthe oscilloscope '|4. The resulting oscilloscope picture is shown inFig. 5. 'Curve (D) .shouldbe understoodcas not yrepresentinga voltage-waveln the manner of waves (A), '(B) and ..(C).,`.but .as merely showing in graphcal'form the frequency responsiveness of the receiver. In -other Words the 'receiver''will be receptive at anyparticular time to the frequency shown'by the curve (D), and if a signal o'fithatirequency appears'at'that instant vit will bereceived and pictured on-.thescilloscope screen.

To produce 'the horizontal .deflection wavefoi Fig. 2 (A) the circuit o'f Fig. l'is employed. A rotating swltchSi'has two conducting .segments d4 and de 4positioned .as shown. .This switch is. connected in lparallelwith the eondenser'C-a. The two .triodes yV1 and'Vz are controlled'by voltages from wave spacers and shapersllli an'd' respectively fapplied t0 .their gridato control 'the ".bias thereof. As lhereinbeiore stated the switchSi rotates synchronously with the scanningcondenserCi.

`Reierringnow to 'the .wave .form (A) .of.l"ig.l2 which isproduced .by the 'circuit ofFig. 1,it .will

'be .seen .that lto produce the portion 'IJ'M' 'the brush of switch "Si is on insulating segment iii. The grid of Viis negative .and no curreritfilows through 'VL "The ,grid "V2 .'is p.ositive,. and current flows through "V2, 4but sufllcient .current reaches C3 to build up a potential thereon (and on thehorizontal plates of the oscilloscope I4) corresponding` to voltage LM.

Over insulating portion d2 of S1, V2 continues tofpass current, but V1 is now operative to hold the voltage constant across C3. This produces the horizontal tread M'N. Over da the conditionl is similar to d1, and thus the wave form L'MfN'P is created.

Upon reaching the intersection cl3-d4, the brushoi rotating switch S1 contacts the conducting segment d4 and the condenser C3 immediately dischargesA to give the return sweep which is blanked by wave C of Fig. 2. No further potential isfbuilt up across the condenser C3 until ds is reached. (V1 is inoperative during the entire time except while the brush of switch S1 is on portion dz.)

When d5 is reached, ,V2 issuddenly keyed out. All `thecurrent now reaches C3, and a very rapid build up (or rapid sweep FG) is obtained. This build-up will reach an amplitude R' as shown in Fig. 2 (A) equal to P'. Upon contacting de the condenser C3 again discharges. The desired wave pattern (A) is thus created. It might be mentioned that V1 has for its function the production of the horizontal tread MN, and V1 is only operative during this interval MN (di). The function of V2 is to reduce the voltage applied to Ca during all times except Q'R (ds). V1 is inoperative except during d2. V2 is operative except during d5. R3 and R4 should preferably be low compared to R1 and R2 so that the time constant is not appreciably affected by the action of V2.

While I have shown and described the invention as a monitoring system, it is contemplated that the apparatus disclosed may be employed with a transmitting arrangement to result in improved jamming of an enemy station operating on a particular frequency. By alternate blocking of the receiver and transmitter in a manner described in my co-pending application 471,237, filed January 4, 1943, the two indications may be made to appear on the oscilloscope screen, and they may be separated into Waves having opposite slopes on the lower portion of the screen by properly attenuating the low frequency response of the audio output stage feeding the vertical deflection plates of the oscilloscope. Since the received wave picture and the transmitted Wave picture will thus be in close proximity on the screen, the frequency of the jamming transmitter may be easily adjusted to result in similar wave patterns and thus more eiiicient jamming.

While I have described above the principles of my invention in connection with specic apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of my invention as set forth in the objects of my invention and the accompanying claims.

I claim:

1. A radio receiver system comprising a tunable radio receiver, means ior periodically maintaining said receiver receptive to substantially a single frequency for a predetermined period of time, means for periodically continuously varying alternately with the said maintaining means the tuning of said receiver over a predetermined frequency band embracing the said single frequency, an oscilloscope in the output of said receiver, scanning means for the oscilloscope, a resistance condenser circuit connected to said scanning means, a source of power for the resistance condenser circuit, means for charging and discharging said resistancecondensery vcircuit to derive therefrom a predetermined voltage wave for application to said scanning means, and means for synchronously controlling said tuning varying means, said maintaining means, and said mechanically controlled means.

2. A radio receiver system according to claim 1, further comprising means for manually controlling the selection of the band over which the said tuning varying means is effective.

3. In a radio receiver system .a vacuum tube circuit including a condenser, two triodes, means feeding the outputs of said triodes to said condenser, control means for selectively biasing the grids of said triodes to control the output thereof, a switch, means for controlling said switch to periodically short circuit said condenser, means for synchronizing the operation of said grid biasing control means and said switching means, and scanning tuning means in said receiver circuit, an oscilloscope, means delivering the output of said receiver circuit to one set of deflection plates of the oscilloscope, means deliv ering the output of said condenser to the other set of deflection plates of the oscilloscope, and means for extending the control of the said synchronizing means to include the said scanning means.

4. A radio receiving system comprising a radio receiver, a mechanically-rotated scanning condenser in said receiver, said scanning condenser having a stator combined with a rotor plate formed of two segments of less than each, separated on one side by a cut-out portion extending over an angle of approximately and on the other side by a cut-out portion extending over an angle of substantially less than 180", so that rotation of the rotor will cause the capacity of said scanning condenser, and consequently the frequency received by said radio receiver, to remain substantially constant during the time that both cut-out portions are simultaneously respectively entering and leaving the stator, an oscilloscope, means for delivering the output of said receiver to one set of deflection plates of the oscilloscope, a resistance condenser circuit connected to a second set of deflection plates of the oscilloscope, a source of power for the resistance condenser circuit, mechanically controlled switching means for controlling the charging and discharging of the condenser of said resistance condenser circuit to derive therefrom a voltage wave for application to the said second set of deflection plates of the oscilloscope, said switching means comprising a fixed contact and a rotating contact of substantially circular form and having two spaced-apart conducting segments of less than 90 each, separated on one side by an insulating segment of approximately 180 and on the other side by an insulating segment of substantially less than 180, so that rotation of said rotating contact will permit the condenser of said resistance condenser circuit to charge only during the intervals that the said insulating segments of said rotating contact are in contact with said fixed contact, and means for synchronizing the operation of the said mechanically-rotated scanning condenser and the said mechanically-controlled switching means result in a correlation of the voltages delivered to the two sets of plates of the oscilloscope.

5. A radio receiving system according to claim 4, further comprising two vacuum tubes in said resistance condenser circuit, means for operating 7 thea saidwtubesr to. control: the. charging of said condenser, and,` means for; synchronizing the operationi of the: saidf tube operating means with thefsaidmechani'cally rotated scanning condenser andi theA said mechanically controlled switching means.

6. The combination according to` claim 4 in which: the contacting; areas of` said conducting segments each extends over an angle equal to the: angle of each of said rotor plate segments, and the insulating segments. respectively extend over" angles' equaly to the: angles separating the segmentsiof'therotor` ALBERT PREISMAN.

REFERENCES CITED The following references are of record in the file of1 this patent:

UNITED STATES PATENTS Name Date Bliss June 15, 1926 Number Number Numb er 

